1. Field of the Invention
The invention relates to a method for producing a borehole in the soil. In such a method provision is made in that a drill pipe and a conveyor screw arranged inside the drill pipe are set into rotation and introduced into the soil and in that outcropping soil material is loosened by means of at least one main cutting edge, which is positioned axially in front of the conveyor screw, and is conveyed away by means of the conveyor screw in the inside of the drill pipe.
The invention further relates to a device for producing a borehole in the soil, comprising a drill pipe, a conveyor screw arranged inside the drill pipe and at least one main cutting edge which is positioned axially in front of the conveyor screw for stripping soil material.
The boreholes may serve to produce foundation members and/or pile walls in particular.
2. Related Art
Methods and devices for cased soil drilling, in particular twin-head methods or devices are known. In these methods a drill pipe and a screw that is of the continuous type in particular and located inside the drill pipe, are sunk into the construction site whilst rotating simultaneously. In its end portion the screw has at least one main cutting edge which loosens the soil cropping out in the cross-section of the screw and conveys it to the helical flight of the screw. From the main cutting edge the soil material is conveyed away along the rotating screw in the upward direction. This conveying movement is brought about as a result of frictional effects occurring between the soil material and the surface of the screw flight as well as between the soil material and the inner wall of the drill pipe.
A method of such kind is known for instance from EP 1 394 351 B1 (corresponding to U.S. Pat. No. 6,994,494). It is especially suitable for being applied in unfixed soils, such as gravel and sand, in cohesive mixed soils and/or in soils lying below ground-water level, because in this case the production of an artificial superimposed water-load can be avoided.
However, in twin-head drilling it turned out that under certain circumstances only a comparatively low drilling progress can be attained, which is quite often accompanied by a comparatively high wear occurring on the inner wall of the drill pipe and on the conveyor screw. This effect can be encountered in particular in poorly graduated soil granulations and/or in the case of coarse gravel being existent.